Abstract: To learn the deformation and pressure variations of surrounding rock in the widened sections of super-large tunnel, the Caijianweishan #2 tunnel in Xiamen is studied as a typical example. In different widened sections of the tunnel, various deformation control measures, like optimizing construction method, increasing step sequence, and closing the loop as early as possible are taken, and on-site monitoring and comparative analysis for deformation, surrounding rock pressure, and supporting axial force are carried out. The results show that: (1) In tunnels with super-large cross-section, the total amount and duration of surrounding rock deformation increase with span, but its deformation rate does not change with construction method. (2) The peripheral convergence of surrounding rock near the vault is larger than that at the arch waist, and the total amount difference of their convergence increases with the excavation span, thus the deformation of surrounding rock at the vault should be focused on in construction. (3) As deviatoric pressure is produced at the vault in the middle of two tunnels, more attention should be paid to the stress monitoring of the middle rock side. (4) The analysis results verify that the construction method optimization is effective to control deformation in this super-large section tunnel. 

Key words: super-large section tunnel, three bench method, double side drift method, deformation control of surrounding rock, surrounding rock pressure, monitoring analysis